If the inside of your car smells or starts to smell then you need
to replace the aircon filter:-
http://www.forfour.co.uk/forum/index.php?topic=150.0You can also buy anti-bacterial spray in many different aroma's...
like chewing gum, or roses, or spring flowers etc etc.. that you can
spray up into or ever onto the filter.
Be aware that these sprays can be very strong/overpowering, so
only use a few sprays...or even dilute it with water and put that
into a small handy plastic pump bottle.
The other choice is to get one of those small round 'can' air fresheners
and stick it up under the lower facia panel beneath the heater controls,
or pop it into the front cup holder.